This Is Why Your Scalp Hurts When Your Hair Is Dirty

There's science behind why day three hair hurts.

We’ve all tried to extend a blowout past its natural lifespan or relied a little too heavily on dry shampoo during an exceptionally busy week. We know it’s bad for our hair, we know it weighs it down — we know, we know, we know. But why does your scalp actually hurt when it comes time to wash all that grease out of your hair? Science has the answer.

If you notice an ache or tenderness as you let your tresses down in the shower, it’s because oils your scalp produce naturally build up around your hair shaft. This can lead to the overgrowth of yeast on your scalp (yes, we’re grossed out, too). In an interview with Glamour, Dr. Joshua Zeichner, a New York City-based board-certified dermatologist, explained how this can lead to inflammation.

“In some patients, inflammation may manifest most with an ache,” Zeichner told Glamour.

The inflammation can also cause redness, itching or scaly skin. Though it sounds truly revolting, it doesn’t mean you have a yeast infection on your head. In fact, it’s a totally different kind from the better-known (but equally unpleasant) Candida yeast.

The yeast on your scalp is called Malassezia yeast, and lives on everyone’s bodies, according to Zeichner. When there’s more yeast than normal — for example, when you need to wash your hair — your body becomes more sensitive to it. This is what can cause the aching, itching or discomfort, Dr. Cynthia Bailey, a diplomat of the American Board of Dermatology and president and CEO of Advanced Skin Care and Dermatology, Inc., told Glamour.

Another thing to note: When your hair is oily, you’re more likely to pull it back in a tight ponytail or bun, which can also cause discomfort, Bailey said.

So what’s the solution? Well, wash your hair. Zeichner suggests reducing yeast levels with an anti-fungal shampoo like Nizoral 1 percent shampoo, found at drugstores. You can also use a tar extract-based cleanser like Neutrogena’s T-Gel to reduce inflammation further.

“Remember that while these shampoos may wash hair, they should really be used as scalp treatments,” Zeichner told Glamour.

This means you shouldn’t apply them anywhere but your scalp, and make sure to lather them for “the length of time that it takes to sing the alphabet.”

Once you rinse the treatment off, you can shampoo your hair as normal.